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The Human Body
The Human Body
Introduction
Human body
– Nervous system
– Musculoskeletal system
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Muscular forces
Muscle extension and contraction
Complex system of muscles and bones
– Produces movements
– Cardiovascular system
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Heart
Blood vessels
Respiratory system
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human Body
The Nervous System
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Central Nervous System
– Brain
– Spinal Cord
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Peripheral nerves
– Efferent nerves: Motor nerves
– Afferent nerves: Sensory nerves
SomaticNervous
System
– Connects organism
withoutside world
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Neuron
The structural and functional unit of all nervous
tissue (nerve cell)
Function
Nerve impulses transmitted through
nerve cells
Structure
• Soma – Cell body
• Axon – Conduct nerve impulses away
from cell bodies
• Dendrites – Mediate impulses from other
neurons to the soma
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Function of nerves
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Control system
Regulates external and internal activities
Monitors a variety of sensations
Factors influencing the working of a neuron
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Sensitivity of stimuli
Ability to transmit a stimulus
– Stimulation of nerves
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Impulse travels along nerve fiber
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Muscle innervation
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Every muscle is connected to the brain
– Efferent nerves or motor nerves
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Motor nerves carry impulses to skeletal muscles
– Afferent nerves or sensory nerves
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Sensory nerves conduct impulses back to the brain as signals
Each nerve fiber serves to innervate several muscle
fibers
Motor unit
– Includes motor neuron and the muscle fibers that it
innervates
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Motor Unit
§ Group of muscle fibers innervated by branches
of same motoneuron
§ Size depends on function of muscle
- May vary between and within muscles
- Small in size where precision movement is
required
§ Eye muscle à10 fiber in each motor unit
- Larger in coarse acting muscles
§ Limb muscleà single motoneuron can supply
more than 1900 fibers
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Reflexes
– Controls movement and activity
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Reflex consists of three parts
1. An impulse travelling along sensory nerve
2. Intermediate neurons, passing impulse to motor nerves
3. Final impulse to activate muscle
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Blinking is a reflex used to protect the eye
– Stimulus: Unexpected movement
– Impulse travels to the brain
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Message passed to motor nerve
– Motor nerve operates muscles of the eyelids
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Skilled Work
Grasping Operation
1. Use of visual information to direct
movement toward object to be grasped
2. Information from eye is transferred to
brain
3. On basis of visual information
- Brain decides the next move
4.
When object is grasped
- Pressure sensitive nerves send new
signals to the brain
- Operator can adjust finger pressure
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Nervous System
Conditional Reflexes
§ Practice of movements for a long time
§ Complete movement pattern becomes engraved in
the brain
§ Coordination and delicate adjustment of muscular
movements
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Continuous stream of sensory information reaches
motor coordination centers
§ Skilled work
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Learning eliminated conscious control
Movements are automatic
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human Body
The Musculoskeletal System
Types of muscles
– Cardiac Muscle
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Heart muscle
– Skeletal Muscles
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Attached to the bone
– Smooth Muscles
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Internal organs and walls of blood vessels
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human Body
The Musculoskeletal System
Skeletal Muscles
• 400 muscles within the body
• Constitute approximately 50% of total body
weight
• Attached to the bone by tendons and crosses one
or more joints
• Controlled by the voluntary nervous system or
somatic nervous system
Function
Generate movement around a joint
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human Body
The Musculoskeletal System
Structure of muscles
• Constitutes of large number of muscle fibers
- Number of fibers depends on muscle size
• Connective tissues bind fibers to form bundles
• Attached to the bone by tendons and crosses one
or more joints
• Controlled by the voluntary nervous system
Function
Generate movement around a joint
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human Body
The Musculoskeletal System
Structure of Muscle
– Group of muscle fibers constitute a muscle
– Muscle fibers subdivided into components that
provide the contractile mechanisms
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Myofibrils
Protein filaments
– Filaments
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Allows muscles to contract
Types
– Thick filaments
– Thin filaments
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Sliding filament theory
– Filaments slide over each other
– Allows muscle length to change during contraction
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Musculoskeletal System
The Human Body
The Musculoskeletal System
Muscle contraction
– The ability of a muscle to shorten to about half its
normal resting length
– Work done by a muscle in a complete contraction
increases with its length
– Each muscle fiber contracts with a certain force
n
Strength of entire muscle depends on sum of muscle
fiber forces
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Musculoskeletal System
Muscle contraction
– Maximum strength of human muscle
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Muscle cross section of 100 mm2 can develop a force
of 30 to 40 Newtons
– Inherent muscle strength depends on the muscle
cross-sections
– Maximum muscle strength
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At the midrange of the motion
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Musculoskeletal System
Regulation of muscular effort
– Muscle fiber made to contract by incoming nervous
impulses
– Amount of muscle strength depends on number of
nervous impulses
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Excitation of the number of motor nerve cells
– Speed of muscle contraction
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Speed at which force is developed during a given
interval of time
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Heavy work
§ Activity that requires physical exertion
§ Characteristics
- High energy consumption
- Severe stresses on the cardiovascular system
§ Energy consumption and cardiac effort
- Set limits to performance of heavy work
- Used to assess severity of physical task
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Physiological Measures
Heart rate
- Normal 72 - 80 beats per minute (bpm)
Oxygen consumption
- Average resting 0.25 - 0.3 liters per
min (L/min)
Body temperature
- Normal 98.6º F
Blood pressure
- Normal 120/80 mm Hg
(systolic/diastolic)
Respiration (ventilation) rate
Blood
Metabolites concentration in saliva
Urine
The Human Body
The Cardiovascular System
Metabolism
n
Conversion of chemical energy (food energy) to mechanical
energy and heat
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Basal Metabolism
– The rate of metabolic activity of a subject after 12 h fasting and
8 h resting is called Basal Metabolic Rate (BMR)
– Energy consumed at rest
– Steady energy consumption
– All chemical energy from nutrients is converted into heat
– Factors influencing basal metabolism
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Gender
Size
Weight
BMR maintains
1) Body Temperature
2) Body Functions
3) Blood circulation
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Energy expenditure
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Energy expenditure is required for the muscle contraction
process
Unit of measurement: Kilojoules (kJ)
Assessment
– Direct method
§
Measurement of heat (energy) generated by a person in a
calorimeter
– Indirect method
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Recording oxygen uptake required for oxidation of nutrients
– 1 liter of oxygen consumed = 20 kJ (5kcal) energy released
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Energy Expenditure
– Two basic types of metabolism
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Aerobic
– More efficient, but very slow
– Sustained for a long duration
Example: Distance Running
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Anaerobic
– Very inefficient, but is much quicker
– Work performed for no more than few minutes
Example: Sprinting
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human Body
The Cardiovascular System
Energy Expenditure
Sub Maxim al - Oxygen Consum ption Vs. Tim e
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minut e s
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The Human Body
The Cardiovascular System
Heart Rating Guidelines
– Measurement of oxygen consumption and energy expenditure is very
expensive
– An alternate and indirect method of measuring energy expenditure is
heart rate
– The heart pumps the blood carrying oxygen to the working muscles, thus
the higher the level of energy expenditure, the higher the heart rate level
– Instrumentation: heart rate monitor, $100, easy to use
%HRmax = (HRave - RHR) / (Est. HRmax - RHR) * 100%
– Est. Hrmax = 220 - age
for females
– Est. Hrmax = 205 - age/2 for males
Guideline: Never exceed 1/3 of an individuals max HR or max oxygen
consumption!!
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human Body
Subjective Ratings
Subjective Ratings of Perceived Exertion (RPE)
– An even easier way of rating workload, Rating Verbal Anchor
replacing the expensive machinery
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No exertion at all
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extremely light
– Borg 10 & 20 Scales
Borg’s 1967 RPE Scale with
Verbal Anchors (20 Scale)
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FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
very light
light
somewhat hard
hard
very hard
extremely hard
maximal exertion
The Human Body
Measure
Equipment
Heart rate
- Heart rate monitor
Blood pressure
- Blood pressure monitor
O2 consumption
CO2 production
Respiratory quotient (RQ)
- Beckman Metabolic Cart (MMC)
Tidal volume
Minute ventilation (Ve)
Breath/min
Electromyogram (EMG)
- Physiograph
- Preamplified surface electrodes connected to a PC (via hardware and software)
Electrocardiogram (ECG/EKG)
- Electrocardiograph (5 lead, 9 lead)
Lung capacities - FEV1.0, FVC
- Spirometer
Static strength
- Grip strength
- Pinch strength
- Back, composite strength
- Hand grip dynamometer
- Pinch gauge
- Load cell
Dynamic strength
- Isokinetic
- Isoinertial
- Cybex, LIDO
- Air Force 6 ft incremental lift
Range of motion
- Goniometer
Temperature (oral, skin)
- Thermometer, temp probes
- Flexometer